First, I'd just increase the row height so that it looks like the rows are
double spaced. (Inserting empty rows can screw up other things--pivottables,
filters, charts...
But if you want...
Sort the data the way you want (we'll add the blank rows later)
Find an empty column
put 1 in the first row (with data) in that column
Put 2 right under it.
Now select those two cells and drag down the length of your data.
You'll see a nice sequence of numbers--1 through the number of rows you need.
Select that big list of numbers
edit copy
select the cell under the list
edit paste
now you have two sets of numbers 1-### and then 1-### again.
Now sort by that column.
Delete the column when you're done.
